I like to feed wild birds, and many visit my home. Unfortunately, local cats misunderstand the concept of wild bird feeding, and try to feed on them. I put feeders up high to avoid this, but some birds feed on the ground on scraps which other birds drop.

I do not own the cats, and I do not know who owns them.* So, I cannot put bells on them, which is the normal solution. I considered one of those high pitched noise makers which dogs and rodents can hear, but not humans. However, this is likely to keep the birds out, as they have a wider range of hearing then we do.

Is there a simple solution? Please assume no damage is to be done to the cats.

*(Of course, no one truly owns a cat. It agrees to spend time with with you on condition that food and other comforts are supplied to its satisfaction.)

If you're out there at the time, a spritz from a water bottle will help deter a cat, but I suspect there is very little you could do when you're not actually there. Hunting is normal cat behaviour and whilst you're doing a lovely thing by feeding the birds, you're actually encouraging the cats by having the birds congregate in your garden.

You could rig up a pie plate or something to sit under the feeder to keep the bird feed from falling on the ground. Or build a chicken-wire (or screen wide enough for the feed, but not the birds, to get through) dome on the ground to keep the birds from feeding on the fallen bird feed.

You'll have a hard time keeping cats from hunting birds at ground level. I think you'll have more luck keeping the birds from feeding there.

We feed three ferals who came attached to the house we move into, and I also like to put out bird food. However, providing regular, constant meals for the cats has really dulled their hunting instincts. They know they have another meal coming soon, so they lie around watching the birds but make no attempt at capture. Also, the feeders hang from the top of the deck, putting them far out of the cat's immediate reach.

Doves - the most common ground-feeding birds - are kinda on their own, though. Still, I never find telltale feathers in our yard.

We feed three ferals who came attached to the house we move into, and I also like to put out bird food. However, providing regular, constant meals for the cats has really dulled their hunting instincts.

That. We feed a pair of ferals (more like "outdoor communal cats", really.. they're sweethearts.), and they've been stalking critters less as a result.

Sorry, I was sitting in my mother-in-law's house in the middle of nowhere with no internet for a couple of days. Strange to be isolated from the net for so long - you suddenly realise how it has become integrated into life.

Thank you all for your ideas. I don't think a motion sensor will work as it will sense the motion of birds too and scare them off. In essence, the other ideas amount to physical prevention or bribery.

However, bribing cats with food is not a sure thing. In the past, I knew a cat which was fed by three separate households, each of which thought they "owned" her. Her triplicity was only discovered when one "owner" met her in a neighbour's house, and then asked around. It's a version of Parkinson's Law - a cat's appetite expands to meet the available food.

Asking a cat not to hunt birds goes against the natural order of things.

This would be a fair point if anyone here had proposed asking the cats not to hunt. The OP asked about preventing them from hunting in a particular spot. There are lots of things that are part of the "natural order" that can prevent or deter instinctive behaviour.

I always thought that a cat doesn't really stand a chance to catch a healthy bird. I guess it depends on the kind of bird.

Heck, I remember having a DOG who would occasionally catch a bird. The result of a bird feeder which spilled seed on the ground underneath some evergreen trees with very low branches. The dog would trap the foraging bird underneath the tree where it couldn't fly away.

I know this is an old thread, but I found it odd that no one suggested putting collars with leetle dinky bells on the nice kitties. That way you don't take away their fun, just handicap them a little bit.

Sure, it won't be easy to catch/collar them, but you'll only need to trap 'em once.

Not in my (admittedly limited) experience: adult cats tend to prefer what they're used to eating.

My experience is based on my own cats, who get plenty of cat food, and who enjoy chasing and catching birds, mice, etc. but haven't shown any signs of interest in eating what they catch. (The fun thing is to bring critters inside, alive, to play with.) So a well-fed cat may still pose a threat to birds.

Some birds are natural ground foragers, and taking advantage of an abundance of seed on the ground due to a human-controlled feeder does not make them weak or stupid to be picked off. They are simply easier targets, sadly.
To the OP...as Thudlow points out, cats will hunt even if well-fed. To avoid giving them easy pickings, get rid of the bird feeder.